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Understanding the mechanisms involved in the building up of organic matter pools with long residence time in soils is fundamental for the comprehension of carbon dynamics. As organic matter persistence depends on environmental conditions and soil properties, both pedogenic processes and factors should be key elements for identifying the link between organic pools and stabilization mechanisms.In the Ligurian Alps, an area where pedodiversity is large, we evaluated the importance of two soil formation factors, vegetation and parent material, and consequently pedogenic processes and soil features, on organic matter stabilization in forest soils. We thus selected 20 profiles, developed on different parent materials and forest stands, which ranged from Regosols, to Cambisols, to Chernozems/Kastonozems, to Podzols and Luvisols/Alisols. In the mineral horizons, we determined the soil physico-chemical properties and fractionated organic matter into labile and stabilized (recalcitrant and mineral-bound) pools using NaClO followed by HF treatment.Soil and organic matter characteristics were primarily explained by the parent material and soil type, while vegetation affected organic matter quality but not the total amounts. The labile and recalcitrant organic pool proportions were linked to parent material likely through its effect on pH and other microenvironment characteristics. The mineral-associated organic matter instead followed a pedogenic pathway, with higher percentages of stable organic carbon in illuvial B horizons from Podzols and Luvisols/Alisols. In the study area, therefore, the most developed soils were relatively more resilient for organic matter conservation than less developed soils, which are more prone to C losses.

Because of extensive Pleistocenic glaciations, which erased most of the previously existing soils, slope steepness and climatic conditions favoring soil erosion, most soils observed in the Alps (and in other mid-latitude mountain ranges) have developed during the Holocene or Late Glacial period.However, in few sites, particularly in the outermost sections of the Alpine range, Pleistocene glaciers covered only small and scattered surfaces, and ancient soils could be preserved for long periods on stable surfaces. In many cases, these soils retain good memories of Quaternary periglacial activity, which have never been characterized on the Alpine range. Based on both geomorphological and pedological interpretations, this work aims to investigate these environments, providing, therefore, new evidences to support paleoclimate reconstructions on the Alps.We described and sampled soils on stable surfaces in the Upper Tanaro valley, Ligurian Alps (Southwestern Piemonte, Italy). The sampling sites were between 600 to 1600 m a.s.l., under present day lower montane Ostrya carpinifolia, montane Fagus sylvatica forests or montane heath/grazed grassland, on quartz-rich substrata.The surface morphology often showed strongly developed fossil periglacial morphologies such as large-scale patterned ground, blockfields/blockstreams or solifluction sheets.The soils preserved in such Quaternary periglacial landforms normally showed stratification of different layers (units), separated by structural discontinuities, evidencing different depositional settings and different pedogenic development degree. A strong cryogenic granulometric sorting characterized all the observed soils/paleosols, with silt-enriched horizons and lateral differentiation of sand-and stone-rich parts and fine enriched ones; organic matter was irregularly distributed at depth as a result of past cryoturbation. Compact and dense layers with strong platy/lenticular structural aggregation, wedge casts and large-scale cryoturbations were described below fixed depths in all soil profiles. Thus, surface morphology and soil properties suggest the presence of permafrost during cold Pleistocene phases, with two main active layer thicknesses at 60-120 and 100-160 cm depths respectively.

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Soil erosion depends mainly on its intrinsic vulnerability (soil erodibility), which is represented by the K factor of the RUSLE equation. Soil erodibility is strictly related to soil structure, which depends mostly on soil particle-size distribution and organic and inorganic binding agents. Soil erodibility can be estimated through soil aggregate stability measurements. However, the effects of different humus forms on soil erodibility and aggregate stability are poorly understood. In this study, we evaluate the influence of different humus forms on these parameters, and consequently on soil susceptibility to erosion. In the Western Italian Alps, 67 sites were selected on different substrata under common forest vegetation types. In all sites, soil profiles and humus forms were described and classified. Soil samples from the upper mineral horizons (A or E) were analysed (SOM content, water aggregate stability that measures aggregates loss) and soil erodibility K factor was calculated.The results showed that surface mineral horizons in soils with Mor humus were the most susceptible to erosion because they had the greatest values of K and aggregates loss, and their surface mineral horizons were characterized by the lowest SOM content. Conversely, surface mineral horizons in soils with Amphi, which had the greatest SOM content, were the least susceptible to erosion, as demonstrated by the lowest K values and limited aggregates loss. Mull and Moder forms showed intermediate behaviours. Despite a similar SOM content as Mulls, Moders showed a slightly greater aggregates loss. At low SOM content, the aggregates loss increased but it varied significantly among the humus forms. In Moders, SOM variations induced large changes in aggregates losses while Amphi forms were the least influenced by SOM. These results show that the intrinsic characteristics of humus forms, derived from the biological factors to which they are associated, influence soil erodibility and aggregate stability and consequently soil susceptibility to water erosion.

Background and Aim: Biotic and abiotic factors contribute in shaping the distribution through the soil